Effect of the silica texture on grafting metallocene catalysts

A series of hybrid supported catalysts was prepared by sequentially grafting Cp2ZrCl2 and (nBuCp)2ZrCl2 (1:3 ratio) onto synthesized xerogel, aerogel and commercial silicas. Supports and catalysts were characterized by Rutherford backscattering spectrometry, energy-dispersive X-ray scanning electron microscopy, atomic force microscopy and nitrogen adsorption. Grafted metal content laid between 0.15 and 0.5 wt.% Zr/SiO2. All the systems were shown to be active in ethylene polymerization with methylaluminoxane as the co-catalyst. Catalyst activity and molecular weight were shown to depend on the textural characteristic of the silicas, namely grain size and pore diameter. The highest activity in ethylene polymerization (ca. 5310 kg PE mol Zr−1 h−1) was obtained with the supported catalyst using commercial silicas with average particle size around 50 μm. Particles with sizes of 80–90 μm obtained less activity. Resulting polymers were characterized by gel permeation chromatography and differential scanning calorimetry.

Graphical abstractA series of hybrid supported catalysts was prepared by sequentially grafting Cp2ZrCl2 and (nBuCp)2ZrCl2 (1:3 ratio) onto synthesized xerogel, aerogel and commercial silicas. Grafted metal content, catalyst activity and polyethylene molecular weight was shown to be dependente on textural properties of the silica support. Figure optionsDownload full-size imageDownload as PowerPoint slide